1. Field of the Invention
The present invention relates to an optical element and an optical switch used in technical fields such as optical communication and optical signal processing.
2. Description of the Related Art
Transmission bandwidth for optical communication has been constantly expanding in recent years, and this promotes increases in speed and capacity, as well as being coupled with advancement in wavelength division multiplexing technology. Optical switches are necessary to architect hardware infrastructure of optical fiber network in backbone network. Of optical switches, those available with single-mode optical fibers are necessary. This demands that light be made switchable irrespective of the polarized state of light such as TE mode and TM mode. As solutions for the demand, there have been proposed a mechanical drive system such as so-called MEMS (micro-electromechanical system) based on a switching of light by moving a micro-mirror, and a thermooptical drive system based on heat-induced variation in refractive index and resultant changes in the direction of propagation of light.
The mechanical drive system or thermooptical drive system, however, suffers from a problem in that switching destinations of optical signals takes a relatively long time, on the order of a millisecond (msec), and that the limit speed of switching is therefore slow. Faster optical switches are therefore desired in recent trends in further advancing network speed.
One known method of rapidly varying the refractive index is the use of the electrooptic effect (electrooptic effect system). Use of such an electrooptic effect system makes it possible to rapidly vary the refractive index within an extremely short time on the order of nanoseconds (nsec) to microseconds (μsec), and consequently makes it possible to realize an optical switch capable of an extremely rapid operation.
[Patent Document 1] Japanese Patent Application Laid-Open No. 2003-177262
The refractive index in the optical switch based on electrooptic effect can be changed by applying a variable voltage to an electrooptic effect film in which light propagates, under proper adjustment of the voltage value.
However, a relation between the applied voltage and the amount of change in the refractive index cannot unconditionally be determined, as a result of materials used for an optical element composing the optical switch, dimensional error in element portions, and parasitic capacitance caused by mounting. This inevitably demands severe adjustment from device to device, degrades yield ratio of products, and is a major reason for rejecting requests for further downsizing of the device.
The present invention was conceived after considering the above-described problems, and an object thereof is to provide an optical element capable of readily and accurately controlling the refractive index of an electrooptic effect film, and is adaptive to further downsizing, and also to provide an optical switch applied with the optical element.